The Ophiurida are an

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

echinoderm An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as ...

s within the

class Class, Classes, or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used d ...

Ophiuroidea Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomot ...

. It includes the vast majority of living

brittle stars Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomot ...

Characteristics

Ophiurida have

bursa Bursa () is a city in northwestern Turkey and the administrative center of Bursa Province. The fourth-most populous city in Turkey and second-most populous in the Marmara Region, Bursa is one of the industrial centers of the country. Most of ...

e for respiration and excretion, and dorsal and ventral arm shields are present and usually well developed. Arms are unbranched and incapable of coiling vertically. Most are five-armed, some with 4 or 6 arms as an abnormality, but others properly bear six or seven arms. The madreporite is on the oral surface. The digestive glands are entirely within the central disc. They move their arms side to side by means of

ball-and-socket joint The ball-and-socket joint (or spheroid joint) is a type of synovial joint in which the ball-shaped surface of one rounded bone fits into the cup-like depression of another bone. The distal bone is capable of motion around an indefinite number of ...

s. Tropical species tend to contrast color from the environment, but most others prefer to blend in. These biochromes do not include echinochromes.

Systematics and phylogeny

There is currently no consensus as to the subdivision of the Ophiurida. The order has been divided into the following suborders and infraorders * Ophiomyxina *

Ophiurina Ophiurina are a suborder of brittle stars containing the majority of living brittle star species. Characteristics Ophiurina contain a large number of ophiuroids with characteristics ranging from skin just covering the disk, the presence or abs ...

** Hemieuryalina ** Chilophiurina **

Gnathophiurina The Gnathophiurina are a group of Ophiuroidea mostly treated as suborder (but at first as an order Gnathophiurida, and sometimes as infraorder of OphiurinaSmith, A.B.; Paterson, G.L.J. . Ophiuroid phylogeny and higher taxonomy: morphological, ...

** Ophiodermatina ** Ophiolepidina Another classification scheme divides it into the following suborders: * Chilophiurina Matsumoto, 1915 * Laemophiurina Matsumoto, 1915 * Ophiothricidae Ljungman, 1867 (= Ophiotrichidae) *

Müller & Troschel, 1840 Another classification scheme divides it as: * Chilophiurina * Laemophiurina *

Ecology

Ophiurida have a world-wide distribution range and are found in oceans in different depths. Most of them are

herbivore A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...

s or

detritus In biology, detritus ( or ) is organic matter made up of the decomposition, decomposing remains of organisms and plants, and also of feces. Detritus usually hosts communities of microorganisms that colonize and decomposition, decompose (Reminera ...

feeders.

References

Ophiuroidea Extant Devonian first appearances {{Ophiuroidea-stub